The present invention generally relates to deflection yokes, and in particular, to deflection yokes for use with monochrome or color television receivers, wherein vertical deflection windings are toroidally wound on a ferrite core in a manner which substantially reduces or eliminates undesirable ringing and other unwanted distortion phenomena.
In conventional monochrome and color television receivers, a cathode ray tube (CRT) is provided with a deflection yoke assembly for deflecting electron beams generated within the CRT to produce a display raster. In the case of color television receivers, the deflection yoke performs the additional function of converging the beams provided by three separate electron guns. Typically, deflection yoke assemblies include a frusto-conical ferrite core dimensioned to surround the relatively narrow neck portion of the CRT which joins the flared portion of the tube envelope. Frequently, the deflection yoke includes a pair of diametrically opposed toroidally wound windings on the ferrite core for causing vertical deflection of electron beams, while a pair of saddle-shaped windings disposed between the interior surface of the core and the external surface of the envelope, provide horizontal deflection of the beam. As the quality of the display is greatly affected by the configuration and location of the deflection windings, much effort has been expended in developing winding distributions which provide displays of superior quality.
Since the path distances travelled by individual electrons of the electron beam vary according to the location on the screen to which the beam is directed, use of uniform magnetic deflection fields results in a distorted raster. Accordingly, non-uniform fields are used to obtain a non-distorted raster. Such non-uniform fields are produced by altering the shape of the deflection windings, as well as, the distribution of turns within individual windings. Cosine windings, wherein the turns density varies according to the cosine of an angle, constitute one form of distribution frequently used. Other winding distributions may also be used.
Once an acceptable winding distribution has been identified, it is necessary for a deflection yoke manufacturer to develop a method for accurately and economically reproducing the desired distribution over a large quantity of cores. One technique developed for this purpose is to attach plastic rings having notches, ridges, or pins to either or both edges of the ferrite core. The windings overlap the rings, which serve to maintain the position of the windings relative to the core. The technique is attractive, particularly where the winding distribution is complex, since it is relatively easy to accurately mold a great number of precisely dimensioned notches in the plastic rings. However, the additional manufacturing steps required undesirably increases manufacturing costs.
The invention described in commonly assigned U.S. Pat. No. 4,754,248 overcomes the disadvantages of prior techniques by directly providing at selected locations on the ferrite core a number of notches of preselected depth and width. In winding the deflection windings of the yoke, wire is placed on the core so that each notch is filled before winding commences on the next adjacent notch. The technique of forming notches directly on the core avoids the economic disadvantage associated with the installing plastic rings, and the relatively large dimension of each notch avoids the difficulty associated with accurately forming a large of number of small precisely dimensioned notches directly in the core, since dimensional changes resulting from shrinkage of the core during firing after casting are less significant with relatively larger notches.
The present invention in its broadest aspects relates to the discovery that by providing a conductive wire winding on the ferrite core which follows a helical path about a winding axis along the core, and which follows a winding pattern beginning in the middle portion of each winding segment and which is laid up to intentionally include certain wire crossovers, an improved display characterized by reduced distortion and reduced ringing is provided. Contrary to the prior art, which maintained that a linear wire winding pattern which avoided wire crossovers, provides windings having lower inter-wire capacitance and therefore improved display characteristics, it is now been discovered that improved anti-ringing performance is provided by a center-start, crossover switchback winding pattern which intentionally includes non-linear winding patterns on both notched and unnotched cores.
Accordingly, it is a general object of the present invention to provide a new and improved deflection yoke for use with cathode-ray tubes.
Another object of the invention is to provide a deflection yoke which is economical to manufacture and which is characterized by superior anti-ringing performance.